Tony has it right.
On original install, the pushrod is supposed to be cut to a length that puts the slack adjuster/pushrod angle in relation to one another close to 90 degrees with the brakes applied, and with the brakes adjusted.
In earlier attempts to train drivers, this bit of info was then passed out as how to check your brake stroke..WRONG!!!
First, by eye, a few degrees either side is a whole lot of stroke, and secondly, how do you know the mechanic cut the rod at the right length to begin with? Very inaccurate, for a device so important and that is about an inch of difference between fully right, and fully wrong!
happy coaching!
buswarrior